The commercial processing of photographic materials produces silver bearing photoprocessing solutions containing silver ions. Environmental regulations restrict the discharge of solutions containing silver to concentrations much less than the silver concentrations generally found in silver bearing photoprocessing solutions. Thus the silver concentrations in silver bearing photoprocessing solutions must be greatly reduced before discharge into the environment.
A much improved precipitation process for removal of silver from silver bearing photoprocessing solutions is disclosed in U.S. Pat. No. 5,288,728. The process is carried out in an apparatus having a number of inner surfaces. A mercapto-s-triazine compound, or a soluble salt there of, is used to precipitate silver inside the apparatus. The process and the apparatus are effective in recovering silver from the photoprocessing solutions. However, we discovered that an undesired precipitate forms during the procedure on the inner surfaces of the apparatus. The precipitate tends to stick steadfastly to tubing, filters and other parts of the apparatus. Such a precipitate will build up on the inner surfaces of the apparatus changing the preferred flow characteristics of the process and increasing the pressure necessary to move solution and desired silver precipitate through the apparatus to the collection point. In some cases, clogging of tubing has completely shut-down an apparatus. If the situation goes unnoticed a catastrophic failure may result in the spillage of the photoprocessing solution and loss of the Ag contained in the solution.